This invention relates to the method of implementing a 2-way wireless spread spectrum communication system and more particularly to such a system in a large multi-storied building.
A typical situation to which this invention is addressed is one where a number of people who occupy space in a large multi-storied building operate computers and have a requirement to interact with each other and have access to each others files and an Internet service provider on a real time basis. In order to satisfy this requirement, these computers must be interconnected in some manner and also connected with an Internet service provider. To accomplish this, a network is created which interconnects the computers through a central unit called a server, which acts as a library for files as well as a traffic controller. The computers and server are connected to each other by means of a series of copper wire or fiberoptic cables. As a result, all equipment is fixed in position, not able to be moved and encumbered by masses of cables which may require the construction of special raceways beneath raised floors. These installations are costly, time consuming to install, and difficult to modify. If computers must be moved to new locations in the building, the installation network of cables, raised floors and any other special construction must be abandoned and a new installation created.
In addition, for any of the computers which are part of the network to be connected to an Internet service provider, a router must be connected to the server and this router must also be connected to a special copper wire or fiberoptic telephone company cable. This equipment and cabling is also fixed in position and would be abandoned if the system location were to be changed. In addition, substantial fees must be paid on an ongoing basis to a telephone company in order to connect the computers through the server to an Internet service provider which are exclusive of any fees paid to the Internet service provider for their service.
An alternate to the creation of cabling networks is wireless communication. However, to date this technique has yielded limited results in that effective communication can only be accomplished for short distances and is subject to interference from spurious signals (noise), loss of transmitted signal strength (attenuation), and areas where no signal can be received (null points). Null points result from reflected signals canceling primary signals under certain conditions. All of these types of interference are present in severe form in large multi-storied buildings as a result of phenomena unique to this environment.
Also, in order to create a wireless link to an Internet service provider, a cable must be installed the entire length of the building which leads to an antenna located on the roof of the building. Each computer or server must then be cable connected to this riser cable in order to communicate outside the building with the wireless Internet service provider.
A major purpose of this invention is to provide an inexpensive and reliable communication link between any number of computers located within a large multi-storied building in a fashion that provides an ability to readily relocate, modify and reconfigure the network within the building.
It is a further purpose of this invention to provide the above objects in a system that would also optionally permit a reliable and simplified access to an Internet service provider.
In brief, this invention enables effective communication in large multi-story buildings and meets the objectives recited above by use of two-way wireless spread spectrum transmission and reception involving directional polarized antennas coupled to specific transmission paths. Those paths are the stairwell shafts of the building and a zone outside of the building adjacent to the skin of the building which is accessed through the windows of the building.
The construction of large multi-story buildings makes wireless communication within the buildings unreliable because electromagnetic energy is absorbed and reflected in unpredictable and uncontrollable ways.
It has been found that electromagnetic energy will migrate through a building effectively if it can be coupled to two paths which are available in every building. One of these two paths is the stairwells. The other path is a vertical zone adjacent to the skin of the building. sending signals through these two paths provides markedly better results than do other methods.
To couple energy to these unique paths, two types of directional antennas are employed. Both types of antennas are patch type having an included angle of less than 60xc2x0. These antennas are deployed to generate a radiation pattern which aims them at the locations where access can be had to the stairwells and the windows.
A first patch type antenna is linear polarized with a horizontal electrical field. This provides enhanced signal strength over substantial distances in part as a result of ground reflections.
A second patch type antenna employs circular polarization. The circular polarization enables the receiver to ignore reflected signals and receive only the primary signal. The circular polarization minimizes the existence of null points.
Both types of antennas direct the electromagnetic energy across a floor to access and transmit through stairwells and out of windows along a vertical zone adjacent to the skin of the building and back in other windows. Reception using similar antenna arrangements receive these signals.
The transmission and reception employs a transceiver using a spread spectrum technique that involves a hybrid frequency hopped/direct sequence modulated signal of a known type such as is disclosed in the text xe2x80x9cSpread Spectrum Systems With Commercial Applicationsxe2x80x9d, Robert C. Dixon, 3rd edition, copyright in 1994 by John Wiley and Sons, Inc. publisher at 605 3rd Avenue, New York, N.Y. 10158.
The linear polarized antenna and the circular polarized antenna are connected to a switching circuit at the transmitter and the receiver so that the signals generated are transmitted and received as packets of data alternating between the two antennas. The switch is at a predetermined rate that is greater than the hopping rate of the spread spectrum signal.